1. Field of the Invention
The present invention relates to a door unlocking controller and a control method thereof, which control the unlocking of doors of a vehicle in dependence on a signal from a portable unit.
2. Description of the Related Art
Door unlocking controllers have been developed, which control the unlocking of doors of a vehicle such as an automobile without using a mechanical key or remote control key.
For instance, Japanese Laid-Open Patent Publication No. 2000-73635 discloses a conventional technique 1, in which a wide area capable of receiving a wide-area ID request signal is formed around a vehicle by an electronic radio wave whose operating range is relatively wide. If a portable unit entering this wide area sends back portable-unit ID to the vehicle in response to the wide-area ID request signal, instead of the wide area a narrow area capable of receiving a narrow-area ID request signal is formed around each door. If the portable unit enters any one of these narrow areas, the door in that narrow area is unlocked.
Recently, there has been developed another conventional technique 2. In the conventional technique 2, as shown in FIG. 6, a left-side switch 21L and a right-side switch 21R are provided near the left-side door 26L and right-side door 26R of a vehicle 20 to request unlocking of the doors 26L, 26R. Left and right transmitting-receiving antennas 23L, 23R are provided in the left and right center pillars 22L, 22R of the vehicle 20. For example, if a person 25 who holds a portable unit 24 (portable-unit holder 25) makes the right-side switch 21R on, an ID request signal to request the ID of the portable unit 24 is transmitted from the right-side antenna 23R to a region indicated by reference character Ra. In response to the ID request signal, the portable unit 24 sends back portable-unit ID. If the portable unit ID corresponds to the vehicle ID given to the vehicle 20, the right-side door 26R of the vehicle 20 is unlocked.
In the above-described conventional technique 1, if a portable unit enters any one of narrow areas, the door in that narrow area is unlocked even when the portably-unit holder has no intention of opening that door. Therefore, this does not always meet the unlocking of a door requested by a portable-unit holder, and there is a possibility that an unnecessary door-unlocking operation will be repeated against the intention of a portable-unit holder. In addition, since it is necessary to always form a wide area around a vehicle, it can not be said to be efficient.
Therefore, it is desirable that door-unlocking control be efficiently performed according to the intention of a portable-unit holder.
On the other hand, in the conventional technique 2, either the left-side switch 21L or the right-side switch 21R is operated, so it is found that the holder 25 of the portable unit 24 has an intention of unlocking a door. Thus, in the conventional technique 2, the unlocking of a door can be controlled according to the intention of the portable-unit holder 25. In addition, since an ID request signal is transmitted after either of the switches 21L, 21R is operated, a wide area such as that of the conventional technique 1 does not need to be formed at all times and therefore it is efficient.
However, the conventional technique 2 has a new problem that is to be described below. That is, as shown in FIG. 6, the ID request signal transmitted from the right-side antenna 23R leaks out to the left side of the vehicle 20. For that reason, there is a possibility that the leakage will cause a new safety problem. The leakage region in this case is indicated by reference character Ra′.
For example, as shown in FIG. 7, when a person 30 who does not have the portable unit 24 operates the left-side switch 21L, an ID request signal is transmitted from the left-side antenna 23L to the region indicated by reference character Ra. Originally, even if the person 30 who does not have the portable unit 24 operates the left-side switch 21L, the left-side door 26L will not be unlocked. However, when the portable unit 24 of the portable-unit holder 25 is present within the leakage region Ra′, the portable unit 24 receives the ID request signal and sends back the portable-unit ID. Thus, even when the person 30 who does not have the portable unit 24 operates the left-side switch 21L, the left-side door 26L is unlocked. As a result, there is a possibility that vehicle security cannot be ensured.
There is a technique for avoiding such a problem. For instance, if the right-side switch 21R is operated, an ID request signal is transmitted from the right-side antenna 23R, and at the same time, electronic radio waves of the same strength as the ID request signal are transmitted from the antennas 23L, 23R. In response to the ID request signal, the portable unit 24 sends back the portable-unit ID, and measures the electric field strengths of the two electronic radio waves and sends back the measured electric field strengths. The vehicle 20 judges that the portable unit 24 (i.e., the portable-unit holder 25) is present in the side where the electric field strength is stronger. For example, if the judged side is the right side of the vehicle, it is judged that the portable-unit holder has operated the right-side switch 21R. And if the portable-unit ID and the vehicle ID correspond to each other, the right-side door 26R is unlocked.
However, in this case, the portable unit 24 needs to have the function of measuring the strength of an electric field, so it becomes large in size and costly. In addition, the portable unit 24 needs to measure the electric field strengths of two radio waves transmitted from both sides of the vehicle 20 and send back the measured data of the two electric field strengths, so this will overload the portable unit 24 of small electric capacity.